1. The present invention relates to a movable body driving apparatus in an information processing unit such as an optical head driving apparatus in an optical disk unit.
2. Description of the Related Art
Compared to a magnetic information processing unit, an optical disk information processing unit has advantages that its information storage capacity is remarkably large, that its noise is small, that it is almost not influenced by external factors, that its data storage state is remarkably stable and that it can process information under a non-contacting state to remarkably reduce damages to be caused on its information storage medium and head. Due to these advantages, the optical disk information processing units are widely used in recent years. An example of the optical disk information processing unit is disclosed, for instance, in the U.S. Pat. No. 4,513,406.
In such an information processing unit, an optical head driving apparatus controls the movement of an optical head such that the optical head moves along the radius of an optical disk to carry out information processing operation with respect to the optical disk. The optical head driving apparatus usually comprises a circular bearing whose bearing surface has a circular cross section and an elliptic bearing whose bearing surface has an elliptic cross section. The circular bearing is disposed on one side of a center of gravity of the optical head while the elliptic bearing is disposed on the other side of the center of gravity of the optical head. A first guide shaft passes through the circular bearing, and a second guide shaft passes through the elliptic bearing. The bearings and the first and second guide shafts constitute a guide means of the optical head.
The movement of the optical head is controlled by a linear motor which has a bobbin as a moving portion of the linear motor. A driving coil is wound around the bobbin. The bobbin is positioned symmetrically with respect to the center of gravity of the optical head with the first guide shaft as an axis of symmetry, and the bobbin is connected to the optical head via a proper member to control the movement of the optical head.
As described in the above, in the optical head driving apparatus according to the prior art, the bobbin of the linear motor is positioned symmetrically with respect to the center of gravity of the optical head with the first guide shaft as an axis of symmetry and connected to the optical head. Therefore, a couple of forces are generated at a thrust acting point of the linear motor and the center of gravity of the optical head to generate torsional and abrasive forces between the bearings and the guide shafts. Due to this, service lives of the bearings will be shortened. In addition, balance between a load applied to the circular bearing and a load applied to the elliptic bearing may be lost such that the load on the elliptic bearing is excessively reduced to vibrate a driving system. Due to this, a driving action may not be stable.